Wheel nut indicators are well known, and are considered an important safety feature for large vehicles, for example buses and trucks. A wheel nut indicator is generally in the form of a plastic cap or surround, which fits over the wheel nuts/lug nuts on a vehicle wheel, and which has some kind of pointer. When the wheel nut indicators are installed over the nuts, the pointers will be oriented in a particular direction, for example, the pointers may all be oriented so that they point clockwise around the wheel, or alternatively the pointers of adjacent wheel nuts may point towards each other. The purpose of this is so that any rotation of a wheel nut (because it is becoming loose) will be immediately obvious on visual inspection, because the pointer of the wheel nut indicator will no longer be pointing in the correct direction. As a matter of routine, a driver will carry out a defect check on a vehicle before driving it, and will check the indicators on each wheel. Any problems with loose nuts will therefore be detected and corrected before they become dangerous.
When a wheel is removed for whatever reason (for example to replace the tyre or service the brakes), wheel nuts will be fitted and tightened, and wheel nut indicators will be fitted over the nuts. It is then standard practice to require checking and re-torqueing after the vehicle has been driven a short distance, for example 40-80 km. Generally a paper document is given to the driver, and it is the driver's responsibility to ensure that the vehicle is returned for re-torqueing after that distance. However, there could be times when this paper system is less effective than desired. For example, the document may be lost, a driver change may occur with the paperwork not being handed over, or the wheel might be removed and refitted when there is no driver to hand the paperwork over to. Likewise, repairs might have to be made to dismounted trailers in yards/docks etc.
All of these events could lead to a re-torqueing policy being inconsistently applied. Even if a driver remembers that re-torqueing is required, a situation may arise where he or she incorrectly identifies which wheel is affected, if the paperwork is misplaced or unreadable, for example because it is covered in dirt or grease.
It is an object of the invention to reduce or substantially obviate the above mentioned problems.